The present invention relates to an electromagnet switching device for hydraulic or electrohydraulic directional control valves, especially applied in advancing supports of underground mining equipments with controllable electromagnets accommodated in a case and comprising armature, coil bodies, magnetisable core and switching plunger, whose switching plunger has a switching end which can be coupled to the closing element of a hydraulic valve and an actuating end for manual operation, whereby the effective switching lift of the switching plunger is adjustable.
DE 38 23 681 A1 describes a previously proposed switching device, whereby here the hydraulic valves are actuated as for instance pilot valves via an actuating lever, which is hinged on and on whose free lever end the switching end of the switching plunger acts. For adjustment the armature is formed as an adjusting shaft and joined secured against rotation with an adjusting screw which is screwed into a threaded hole in the free end of the lever. Owing to the lever translation and the adjusting screw sitting in the lever with a fine thread a delicate adjustment of the switching lift is attained. The setting of the angle of rotation is achieved by means of a star wheel, which can move axially but sits fixed against rotation on the free end of the adjustment shaft forming a manual operating end and can be fixed by a rotation securing element to the case. It has been found that the adjustment can be undertaken via the hand operating end of the electromagnet. It is however a disadvantage that the previously proposed switching device requires a lever.
It is an aim of the present invention to simplify an adjustable electromagnet switching device and to make adjustment possible independently of the presence of a switching lever.
Accordingly the present invention is directed to an electromagnet switching device as described in the opening paragraph of the present specification, in which the switching plunger is joined to the armature by a screwed connection and adjustment of the switching lift is facilitated by a relative rotation between the armature and the switching plunger. In accordance with the invention the effective switching lift, which is adjusted or changed exclusively using the parts always present in any electromagnet, can be set independently of the presence of a lever. In a preferred embodiment the armature is fixed in the case, secured against rotation to facilitate the relative rotation. Advantageously the switching plunger is screwed in centrally in the armature and the securing against rotation comprises a pin, arranged off centre, a guide rib arranged off centre, which interoperates with a guide groove on the outer circumference of the armature, a spring key with associated grooves in the armature and the case or similar. Especially the armature has a boring in its front end facing away from the valve, in which a guide pin fastened to the case engages with low play. Obviously in a mechanical reversal the armature can also have the guide pin and the case the boring.
In a preferred embodiment the armature is formed with a preferably multi-stepped blind hole boring with an internal thread and the switching plunger is made in a single part and has an intermediate section with an outer thread, whereby the inner and outer threads are preferably produced as a fine thread, so that with a large angle of rotation only a relatively small readjustment of the switching path or switching lift is caused, and consequently fine adjustment is possible. Furthermore the blind hole boring with the internal thread and the outer thread on the switching plunger can be produced with a small manufacturing outlay.
For simple performance of the relative rotation between the switching plunger and the armature the actuating end of the switching plunger is preferably provided with a multi edged outer profile, onto which a setting element, especially a fixing and adjusting disc with a matching inner profile sits, which can be turned and fixed to the case, whereby preferably the multi edged profile is a hexagonal profile, so that the actuating end for manual operation forms at the same time the adjusting and fixing end for the setting of the adjustment. For fine adjustment the setting element is preferably divided around its circumference into equiangular indexing elements in the form of indentations and/or perforations and/or protrusions or similar, especially preferred in the form of open cut-outs in the rim, which are associated with an arresting means, preferably an arresting pin fixed or which can be fixed to the case. In the embodiment with the arresting pin fixed onto the case the setting element should sit axially movable on the multi-edge profile, so that even when the setting element is lifted from the arrested position the rotation lock between the setting element and the switching plunger remains assured. With the arresting pin removably fixed in the case axial mobility is not required.
As set out further above, the operating end facilitates manual actuation of the directional control valve, e.g. in emergency situations. Previously, in similar emergency situations damage to the switching plunger could arise for instance owing to too high a switching force. In order to avoid this and at the same time to provide the hand actuation in the simplest manner, preferably the operating end of the switching plunger extends out at each adjustment setting over the operating end of the electromagnet case and a top plate is mounted on the operating side, which is provided with cut-outs so that the rim zones of the cut-outs can form a protective collar for the operating ends of the switching plunger and operating ends of the switching plunger can lie sunk in the cut-outs. Advantageously hat shaped bonnets of a flexible, especially elastic material are retained or fastened in the cut-outs, which preferably enclose a press button such as a brass knob as a protective means for the bonnet and/or the operating end. The bonnet, of elastic material, discharges a sealing function against the rough environmental conditions which prevail in underground mining faces. Damage to the bonnet is prevented by means of the press or brass knob.
In a preferred embodiment the switching plungers of the electromagnets are axially aligned to the central axes of the closing elements of the valves and/or a separation plane is formed between the electromagnet case and the valve block housing the valves. Preferably the switching plunger is guided by means of sliding sleeves in the case and/or the iron core and/or that the switching end of the switching plunger engages through a sealing element with sealing lips, so that the environmental influences prevailing underground, especially moisture, coal dust and similar cannot affect the functional integrity of the electromagnets, their switching plungers and the screwed connection between the armature and the switching plunger.